1. Field of the Invention
The present invention relates generally to implantable medical devices; and, more particularly, to a method and apparatus to automatically identify multiple leads and their proper connection to an implantable medical device such as a pacemaker or cardioverter/defibrillator.
2. Background Art
An implantable intravascular lead assembly is often implanted within a patient's body to provide electrical stimulation to the heart. Such lead assemblies may include one or more electrical conductors that are adapted to be suitably connected to a source of electrical energy, which may be a pacemaker or cardioverter/defibrillator. The electrical conductor, in turn, includes an electrode tip that engages the endocardial or epicardial tissue of the heart to provide stimulation and sensing capabilities. The lead assembly may be intravenously inserted through a body vessel, such as a vein, into one or more cardiac chambers, or alternatively, attached to the epicardial surface of the heart. The conductor is sealed from body fluids by a biocompatible and bio-stable insulating material.
In a typical lead assembly, the electrode tip is firmly lodged in, and permanently secured to, the endothelial lining or epicardial surface of the heart. These lead assemblies are referred to as an endocardial or epicardial lead, respectively. Some examples of conventional endocardial and epicardial leads may be found in U.S. Pat. No. 3,348,548 to Chardack, U.S. Pat. No. 3,754,555 to Schmitt, U.S. Pat. No. 3,814,104 to Irnich et al., U.S. Pat. No. 3,844,292 to Bolduc, U.S. Pat. No. 3,974,834 to Kane, U.S. Pat. No. 5,246,014 to Williams, and U.S. Pat. No. 5,397,343 to Smits. A representative defibrillation lead is described in U.S. Pat. No. 6,178,355 to Williams.
With the increased use of multi-chamber pacemakers and defibrillators such as those that provide bi-atrial or bi-ventricular pacing capabilities, multiple leads are required to deliver electrical stimulation to various locations within the heart. With the use of multiple leads that are positioned within one or more small vessels of the body, it has become even more important to minimize lead and lead connector size. As leads become smaller, it becomes increasingly difficult to mark leads with the appropriate identification, including manufacturer identification and/or lead model and serial numbers. This may make it more difficult for a physician to determine which lead is to be inserted into a given port of an implantable medical device (IMD) during an implant procedure.
One solution to providing marking information on lead systems is described in U.S. Pat. No. 5,824,030 to Yang. This patent discloses a single-pass transvenous lead for atrial sensing and pacing, ventricular sensing and pacing, as well as for ventricular and atrial defibrillation. Visual indicators are provided on the lead to identify which one of several distal electrode pairs are being used.
Another solution to properly configuring the leads of an IMD is disclosed in U.S. Pat. No. 5,374,279 to Duffin. The described medical electrical pulse generator includes a switchable connector assembly. The connector assembly is provided with connector bores that are each adapted to receive a medical electrical lead. Electrical connectors located within the bores are arranged such that interconnection of the pulse generator circuitry and the configuration of the electrodes on the leads and/or housing of the device can be altered by means of connector pins.
Yet another method of attaching multiple electrode leads to an IMD is described in U.S. Pat. No. 4,628,934 to Pohndorf. The '934 patent describes an electronic electrode switching circuit that minimizes the number of feedthroughs from a pacer case to a pacer neck that are needed to couple to the pacing lead electrodes. These feedthroughs can be selectively connected to a desired electrode by the physician at the time of initial implantation or any time thereafter. The electronic connection to a feedthrough may be dedicated to a single electrode or electrode pair, or alternatively, the electrodes may be electronically sampled by circuitry in the pacer. The electrode switching circuit may be located in the pacer neck, in an adapter between the pacer neck and a multielectrode lead, or in a multielectrode lead.
Another method for automatically configuring the multiple leads of an IMD is described in U.S. Pat. No. 6,085,118 to Hirschberg. The '118 patent describes an implantable cardiac stimulator with at least two terminals. Each terminal is connectable to an implantable electrode for delivering stimulation pulses to a heart, and/or for sensing cardiac activity signals. The stimulator also has a switch and a control unit which operates the switch, so that one or both terminals are connectable to the pulse generator. The control unit identifies a position status for at least one of the electrodes in response to a signal received at the time of implantation. Although the control unit may use a signal from an electrode to configure the switch, premature sensed events, artifacts and/or EMI may cause the control unit to incorrectly configure the system.
Another identification system is described in U.S. Pat. No. 5,300,120 to Knapp, which involves a passive transponder that may be encoded with a binary value that may be up to sixty-four bits long. This value may be read with a hand-held electromagnetic device that is located outside the body and in proximity to the transponder. The encoded information may include patient demographics, implant data, and manufacturer information.
Another similar mechanism for remotely monitoring device data is described in U.S. Pat. No. 5,626,630 to Markowitz. The disclosed telemetry system includes a remote monitoring station, a repeater worn externally by a patient, and a quasipassive transponder attached to a device implanted in the patient. The remote monitoring station communicates to the repeater to initiate an interrogation routine between the repeater and the transponder to extract patient condition information from the implanted device. When the repeater receives the condition information, it relays it to the remote monitoring station. The disclosed system does not automatically identify leads, calibrate lead-based sensors, or automatically configure leads and/or sensors to an IMD.
U.S. Pat. No. 5,833,603 to Kovacs describes another system for sensing one or more physiological signals within a living body to measure optical, mechanical, chemical, and/or electrochemical properties. The system includes a transponder for wirelessly transmitting data corresponding to the sensed parameter values to a remote reader. Disclosed embodiments utilize temperature sensors, strain sensors, pressure sensors, magnetic sensors, acceleration sensors, ionizing radiation sensors, acoustic wave sensors, chemical sensors, and photosensors. The disclosed system does not include means to automatically identify or configure leads, or to calibrate the lead-based sensors.
Another mechanism for identifying information related to the configuration of an IMD is disclosed in U.S. Pat. No. 5,423,334 to Jordan. The disclosed system provides a characterization tag for attachment to the IMD. The tag circuitry is selectively loaded to store data describing the IMD, and may be read by a probe located outside the body. The system does not store lead identification or configuration information.
Yet another system for storing and transmitting device information is described in U.S. Pat. No. 5,252,962 to Urbas. The disclosed device includes a sensor for use in transmitting a parameter such as temperature from within a living body to a device that is located outside the body. The IMD includes a programmable memory to store user ID data.
While the above publications teach various improvements to the art, they do not address the problem of identifying and configuring multiple leads and/or other implantable devices for use with an IMD.